The long-range goal of the proposed research is to determine the mechanism of active transport through cell membranes. The complete understanding of a membrane transport system in molecular terms will include the isolation and characterizaton of all the components and then the reconstitution of the system from its component parts. We have used biochemical approaches to isolate certain components from bacterial systems that are sensitive to osmotic shock treatment and have partially purfied a leucine-binding component from mouse cells that appears to act as the recognition site for leucine transport. In E. coli, genetic analysis has thus far resulted in a mutational locus involved in leucine transport; a similar analysis with hamster cells in culture has been initiated. We hope to determine the macromolecular components involved in the recognition of an amino acid, its translocation across the membrane and the coupling of the system to cellular energy in both animal cells and in bacteria. In addition, we are examining the regulation of amino acid transport in various primary and secondary animal cell lines to determine if changes in transport activity play a role in malignant transformation events; the regulation of leucine transport in E. coli has been and continues to be the subject of physiological and genetical analysis.